Speaker
Darby Saxbe
Appearances over time
1 episodes
Episodes
1
Podcasts
Quotes & moments
Hands-on fathers lose approximately 1% of gray matter volume across the transition to fatherhood, mostly in the cortex — tied directly to parenting time and investment.
New mothers lose about 2.5% of gray matter volume, affecting both the cortex and subcortex including the amygdala and reward circuitry — a larger and more widespread change than in dads.
By some estimates, dads' daily parenting time has tripled or quadrupled compared to fathers in the 1950s and 60s, with millennial and Gen Z dads spending more time with kids than any previous generation.
Father presence in US homes dropped from 88% in 1960 to 67% in 2005, but has since rebounded to about 76% of children living with a father figure at home today.
UK Biobank data shows that having more children (up to about 3) is associated with better cognitive functioning and machine-learning-assessed younger brain age in middle and older age.
The neuroprotective benefit of parenthood on brain age tops off at around 3 children, after which there is no additional cognitive benefit from having more.
Approximately 10% of new fathers experience depressive symptoms during the perinatal period, roughly twice the general population rate, yet it goes largely unrecognized and unscreened.
Postpartum depression affects approximately 19–21% of new mothers, roughly double the rate in new fathers, which tracks with women having twice the baseline rate of anxiety and depression in the general population.
A Swedish paternity leave reform study found that babies born just after the policy took effect had mothers who filled fewer anti-anxiety medication prescriptions — showing a population-level mental health benefit for moms when dads get more leave.
Darby Saxbe's lab found that new fathers of daughters show a larger drop in testosterone, spend less time caring for babies, and report more parenting stress and worse bonding than fathers of sons.
Darby Saxbe's lab found that couples who fought more negatively during pregnancy experienced more medically complex and risky births, and both partners rated the birth as more stressful.
Darby Saxbe warned that men taking testosterone supplementation while becoming fathers risk suppressing the natural hormonal adaptation that promotes patience and caregiving behavior.
More time spent on housework in the evenings was associated with less cortisol drop at bedtime, suggesting housework disrupts the body's natural stress recovery cycle.
The Aka people of the Congo, a hunter-gatherer society, have fathers who spend extensive time within arm's reach of infants and are heavily involved in caregiving — reflecting the egalitarian, cooperative foraging model.
Research from the Netherlands shows that maternal brain gray matter shrinks again with a second child but in different regions, suggesting brain change is U-shaped — volume is lost then partly regained.
Mother's caregiving drive is turned all the way up at birth — incubating a pregnancy costs thousands of calories and locks in that investment. Fathers' dial sits in the middle by default, ready to rise or fall based on culture, relationship stability, and hands-on practice. This is facultative adaptation: biology that comes online when needed.
Dads who are hands-on lose about 1% of gray matter volume — mostly in the cortex — a change entirely driven by parenting time, not the mere fact of having a child. Moms lose 2.5% across the whole brain because pregnancy already primes them; dads start in the middle and the dial only moves if they engage.
When men become engaged fathers, testosterone naturally drops — and that drop is adaptive. It reduces aggression, increases pair bonding, and promotes nurturing. Men who take exogenous testosterone may be overriding that system, and anecdotal reports from mothers suggest it shows up as reduced patience with their babies.
A Swedish paternity leave reform created a natural experiment: babies born right after expanded paternity leave was introduced had mothers who filled fewer anti-anxiety prescriptions. Darby Saxbe's own lab found the same pattern — when dads get paid paternity leave, moms are statistically less likely to get depressed after birth.
UK Biobank data from thousands of middle-aged and older adults shows that having children is associated with better cognitive functioning and brains that AI algorithms assess as younger. The effect plateaus around 3 kids. The likely mechanism isn't hormones — it's the social integration that parenting forces on you.
Father absence peaked in 2005 when only 67% of US kids lived with a dad — down from 88% in 1960. But that number has since rebounded to 76%. The real picture is more nuanced: many non-residential fathers are deeply involved, and the binary of absent vs. present misses the many shades of paternal engagement.
The brain changes in new dads happen almost entirely in the mentalizing network — the seat of empathy and mind-reading. It grows because caring for a non-verbal infant is a daily workout in reading emotions and solving problems. Simply being a biological father without hands-on care produces almost none of this change.
Darby Saxbe's lab found that fathers of daughters show a bigger testosterone drop, spend less time with their babies, and report more parenting stress and worse bonding — compared to fathers of sons. The likely driver is that dads default to active, rough-and-tumble play styles that feel more natural with boys, leaving them less prepared for daughters.
The best predictor of a mother's postpartum mental health is the support she gets from her partner. When dads are depressed, moms are more likely to be depressed too — and vice versa. Treating paternal postpartum as a zero-sum resource competition ignores the fact that helping fathers directly helps mothers and babies.
Cohabitating couples have measurably linked cortisol levels — when one partner is stressed, the other's cortisol rises too. Relationship conflict tightens that link, amplifying stress rather than buffering it. The fix isn't chemistry — it's learning to fight in ways that calm each other down rather than escalating.
In the Aka of the Congo, fathers spend extensive time within arm's reach of infants — because cooperative net hunting means there's no economic reason to specialize parenting roles. One day's drive away, Kipsigis fathers are prohibited from even picking up babies under one year old, because their riskier slash-and-burn economy demands strict role separation.
Bob Odenkirk described fatherhood as the thing that ended his existential questioning. When your kids are growing up, you don't have to ask what you're here for — the answer is picking up everything between here and the door and making sure they get to school. The meaning isn't found, it's assigned.
Pregnancy physically transforms a woman into a mother through hormones, brain changes, and energetic investment. For fathers, those same transformations are available but conditional on caregiving behavior. The lack of a baby bump means the lack of a biological on-ramp — and the guilt and shame that can come from not yet feeling it.
The most damaging advice new dads receive is that they're biologically useless in early infancy and should step back. This myth drives fathers away from precisely the caregiving behavior that builds their brains, bonds them to their children, and protects mothers' mental health. Richard Reeves argues paternity leave should be available up to a child's 14th birthday.
A successful founder at a business networking event put his hand up not to ask about the IRS or offshore accounts, but to admit he was 6 months into his partner's pregnancy and felt nothing — and was terrified he'd be a bad dad. The room of deca-millionaires immediately erupted with recognition. Other dads had all been there.
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- Health & Fitness 42%
- Society & Culture 42%
- Science 16%
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